RBR850 + RBS850: Ethernet Backhaul in AP Mode - Horrible Performance or bad connection

Hardware Version RBR850
Firmware Version V7.2.6.21_5.0.20
GUI Language Version V3.0.3.10_2.1.30.3
Operation Mode AP

Short version: Even when in AP mode, where the actual routing happens on a different device on the LAN - do I really have to have TWO separate ethernet networks? One for my actual LAN and one that's dedicated solely to the ORBI backhaul?

The more I look at it, it seems to be the case, and I want to make sure.

I thought this would have been simple: I've got an RBR850 + RBS850 system, in AP mode (ie. NOT routing, only as an access point). It has been working well using a wireless backhaul for years. I got around to wiring a dedicated wire to use as a gigabit ethernet backhaul for it, and tried plugging it in to my LAN's star network -- and the Orbi WiFi stopped working. I can get to the configuration HTTP interface, but forget about using WiFi... or anything that's not wired.

I've followed the guide at https://kb.netgear.com/000051205/What-is-Ethernet-backhaul-and-how-do-I-set-it-up-on-my-Orbi-WiFi-System - My setup is most like the bottom configuration, where the RBR850's first LAN port is connected to a switch, and the RBS850's LAN port is also connected to the switch.

From the various posts I've read here, and my own observations, it seems that it's mandatory for the RBR850 and RBS850 to be connected to the switch through the LAN ports.

 

• The yellow WAN port can't be used, or else the router can't connect properly to the satellite
• And the Yellow WAN port MUST be used, or else the router won't connect to the internet, even in AP mode.

The one thing that is not mentioned in any of the diagrams in the Orbi KB article is where "the rest of my network" - including my router - should be connected.

As it's in AP mode, it seems the router should plug into the LAN segment, just like all of the other wired network devices - as all of the services (DHCP, DNS, internet routing, etc) are all coming from elsewhere on the LAN.

So its wired like this:
Internet <-> Router (+DHCP +DNS) <-> Switch <-\

                                  | - RBR850 (LAN Port)

                                  | - RBS850 (LAN Port)

                                  | - Wired Device

                                  | - Wired Device

                                  | - Wired Device

                                  ` - Wired Device

The RBR850's WAN port is unused, I'm using the RBR850's LAN ports are on the router & satellites.

 

... And it's really not working at all. The RBR850 is shows up as disconnected from the internet most of the time, won't do a speed test, but it does talk to the local network. Wireless devices kindof connect but even a ping to the local network has 80% loss.

 

And if I connect the router to the RBR850's WAN port, the RBS850 won't configure the ethernet backhaul, and the RBR850 shows that no satellite is connected.

 

Am I missing something? Is the ethernet backhaul supposed to be on its own completely separate and dedicated network?